High-gain antenna reflectors have been deployed into space for several decades. The configurations of such reflectors have varied widely as material science developed and as the sophistication of technology and scientific needs increased.
Large diameter antenna reflectors pose particular problems both during deployment and post-deployment. Doubly-curved, rigid surfaces which are sturdy when in a deployed position cannot be folded for storage. Often, reflectors are stored one to two years in a folded, stored position prior to deployment. In an attempt to meet this imposed combination of parameters, large reflectors have been segmented into petals so that these petals could be stowed in various overlapped configurations. However, the structure required in deploying such petals has tended to be rather complex and massive, thus reducing the feasibility of such structures. For this reason, parabolic antennae reflecting surfaces larger than those that can be designed with petals typically employ some form of a compliant structure.
Responsive to the need for such a compliant structure, rib and mesh designs have been built, tested, and used. However, such antennae tend to suffer from chording in both radial and circumferential directions. The use of mesh in such a configuration has an inherent disadvantage in diminishing the reflective quality of the resulting parabolic surface. Further, a mesh cannot be made to assume a truly parabolic configuration.
Other antennae designs typically include a center post about which the petals are configured, much like an umbrella configuration. This also affects the reflective quality of the resulting surface, since the center portion typically is the point of optimum reflectance, which is then blocked by the center post. Thus, it is desirable to have a structure that is deployable from a compact, stored position to a parabolic, open position without the use of a center post.
More recently, antenna reflectors have been constructed from carbon fiber reinforced, synthetic material (CFK). Such material may satisfy the requirements for space technology and contour accuracy and, therefore, high performance antenna systems. However, power and performance of such antennae are limited, owing to the size of the payload space in a carrier space vehicle. Very large completely rigid antennas are highly impractical to launch into space, hence the requirements for practical purposes can be satisfied only when the antenna is of a collapsible and foldable construction.
At present, antenna reflectors of the collapsible and foldable variety are of two design types. One type is a grid or mesh type reflector that is folded like an umbrella. The other type includes foldable rigid and hinged petals. Antennas of this second type are available in a variety of configurations, some of which are disadvantaged by the requirement for an excessive number of joints and segment pieces which, owing to the particular folding and collapsing construction, are of different shape and size. Also, the larger the number of hinges and segments, the more complex will be the deployment mechanism and its operation.
Available mesh cloth-covered parabolic rib reflectors form a poor approximation to the ideal smooth, solid paraboloid surface, since the mesh cloth typically is stretched taut circumferentially between each pair of adjacent parabolic shaped ribs. The resulting mesh shape is a triangular gore curved in the radial direction but flat in the circumferential direction. That is, each mesh gore is a singly curved approximation to the desired ideal doubly curved paraboloid gore. For a given paraboloid reflector diameter, the number of ribs used determines the width of each mesh singly-curved gore. Thus, more ribs result in more and narrower mesh gores, with each narrower gore being a better approximation of the ideal paraboloid shaped gore. However, more ribs used for a given reflector diameter results in more mass for the reflector. The resulting mesh cloth/rib reflector concept contains an inherent trade-off of increasing weight versus closeness of the surface shape approximation to the desired true paraboloid shape. Thus, for higher RF frequency usage, the mesh cloth/rib reflector concept requires an increasing number of ribs for a given aperture efficiency requirement.
Thus, there remains a need for a deployable antenna reflector that provides a solid reflector surface upon deployment and that retains its parabolic shape during extended storage.